Striker Joe Garner looks set to be out of action for the rest of the season, while Dominic Iorfa and Muzzy Carayol will both miss Saturday’s trip to Bristol City, however, Cole Skuse is expected to be fit enough to face his old club.
"He’s not any good for this one, as he wasn’t the other night,” McCarthy said when asked about Garner’s fitness.
”He’s got a couple of things that need looking at and he’s unlikely to be any good for the rest of the season, to be quite honest.
"It’s a real blow, it’s been a blow missing him. It’s been a blow having him for the last six or eight weeks not being fully fit and mobile, he’s been wheeling himself out and doing it for the good of the team. Very selfless.
"We’ll wait and see, next week, but he might be missing for the rest of the season.”
The former Preston and Rangers man has been managing a shoulder injury all season but recently it has been a knee problem hampering him.
Asked whether that's the issue likely to sideline the 29-year-old for the season, McCarthy said: "Well, that’ll get announced depending on what happens, the results he gets.”
Iorfa, Carayol and Skuse were unavailable for Tuesday's 3-0 defeat to Hull due to thigh, groin and hamstring problems respectively.
Regarding Iorfa, the Blues boss added: "Dominic’s injured, he strained his thigh, he’ll be one that’s looking at the Birmingham City match.
"Muzzy’s looking at Birmingham as well. It would be easier talking about the players that are fit rather than the ones that are injured.
"Skusey looks like he’ll be OK, Kevin Bru trained today, so thankfully we’ve got a couple coming back.”
Tom Adeyemi remains out with his hamstring injury, while fellow midfielders Emyr Huws, Andre Dozzell (both knee) and Teddy Bishop (hamstring) are out for the season, as are striker David McGoldrick (groin) and keeper Dean Gerken (hip).